The invention relates to a rain sensor, especially for a motor vehicle, said sensor comprising an optical waveguide (22) which can be arranged in a windscreen. According to the invention, the planar holographic coupling elements for coupling and decoupling radiation (4) are formed from layered photo-polymer parts (3) into which volume holograms are integrated. The photo-polymer parts (3) are arranged between the core (1) of the waveguide and the envelope of the waveguide (2), resulting in a simple production method and an increased flexibility in terms of the arrangement of the waveguide (22) in the windscreen.